The present invention relates a plastic control valve for handling the flow of highly corrosive fluids.
Highly corrosive fluids, such as acids, are used in many industries, as in the processing of semiconductor wafers. The corrosive effects of such fluids or liquids is further increased when their application requires that the liquids be heated to temperatures ranging from 24.degree. to 150.degree. C. which will increase the corrosive effect of the fluids.
The handling and control of heated corrosive fluids in measured amounts has been problematic. Known valves having metallic parts are short lived in that their exposure to corrosive fluids will eventually destroy the valves. Furthermore, many applications absolutely require that metallic particles not be permitted to enter into the stream of the corrosive fluids or liquids which may destroy the usefulness of such fluids. The structure of known valves also may have what is known as a dead volume of fluid. That is, fluid may rest within the valve housing such as below the valve seat. The dead volume of fluid makes these valves difficult to flush and clean and may have corroding effects on valve parts.
Construction of valves out of polymers or plastics in combination with metal parts has been attempted to solve these known problems with minimal success. The nature of plastics and polymers allow permeation which will permit corrosive fumes from the corrosive fluids in the valve to work upon the internal operational parts of the valve and similarly render such valves short lived.
The handling of highly corrosive fluids by known valves has by necessity also required difficult and frequent inspection as well as repair to insure the integrity of the control valves. Disassembly of complex valve structures is time consuming and requires down time while the valve is disassembled for inspection and replacement of certain parts.
There is an need for a free draining, corrosive resistent plastic control valve that has a long life and renders itself easy to inspect and repair.